This invention relates to a new method of separating gases using a membrane fabricated from polymers containing a perfluorinated backbone and pendant hydrated metal ionomer moieties, wherein the pendant hydrated metal ionomer moieties are comprised of metal hydrates of alkali metals, alkaline earth metals, or transition metals bound to --SO.sub.3.sup.-.
Membranes have been used to recover or isolate a variety of gases, including hydrogen, helium, oxygen, nitrogen, carbon dioxide, hydrogen sulfide, methane, and light hydrocarbons. Particular applications of interest include the separation of carbon dioxide from light hydrocarbons or other crude oil components as part of the tertiary oil recovery process. In other embodiments, nitrogen or helium is separated from natural gas. Other applications include the recovery of an enriched oxygen stream from air for use in enhanced combustion processes. Alternately, an enriched nitrogen stream may be obtained from air for use as an inert atmosphere over flammable fluids or for food storage.
To separate a gas mixture into two portions, one richer and one leaner in at least one component, the mixture is brought into contact with one side of a semipermeable membrane through which at least one of the gaseous components selectively permeates. A gaseous component which selectively permeates through the membrane passes through the membrane more rapidly than the other component(s) of the mixture. The gas mixture is thereby separated into a stream which is enriched in the selectively permeating component(s) and a stream which is depleted in the selectively permeating component(s). The stream which is depleted in the selectively permeating component(s) is enriched in the relatively nonpermeating component(s). A relatively nonpermeating component permeates more slowly through the membrane than the other component(s). An appropriate membrane material is chosen for the mixture at hand so that some degree of separation of the gas mixture can be achieved.
Membranes are fabricated from a wide variety of polymeric materials. An ideal gas separation membrane possesses a high separation factor (selectivity), high gas permeability, and good temperature and chemical resistance. An ideal membrane also possesses good mechanical properties, that is, resistance to crazing or cracking and minimal creep, under conditions of use. The problem is finding membrane materials which possess all the desired characteristics. Polymers possessing high separation factors generally have low gas permeabilities, while those polymers possessing high gas permeabilities generally have low separation factors. In the past, a choice between a high separation factor and a high gas permeability has been unavoidably necessary. Furthermore, when most polymer membranes are plasticized upon exposure to certain gases and liquids, the gas permeability of the membrane increases with a corresponding decrease in selectivity. A polymer membrane which maintains or improves in selectivity upon plasticization is desired.